1. Field of the Invention
The present invention relates to a process for producing a semiconductor device, and more specifically to the process for producing the semiconductor device, with making use of a semiconductor of a III group nitride compound.
2. Description of the Background Art
In recent years, there is developed a semiconductor device with making use of a semiconductor of a III group nitride compound, for an object of such as an operation thereof to be speed up, a stable operation thereof under an environment at a high temperature, or the like (refer to a patent document 1 as mentioned below for example). Moreover, as such the semiconductor of the III group nitride compound, there are used such as gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN), or the like.
Further, in a case of producing such as a MOSFET (metal oxide semiconductor field effect transistor), with making use of the semiconductor of the III group nitride compound, it becomes required a process to activate an impurity, for such the impurity to function as a dopant, which is implanted into such as a source region, a drain region, or the like, regarding a semiconductor layer (refer to nonpatent documents 1 to 3 as mentioned below for example). Furthermore, for such the process, there is made use of an annealing process therefore with making use of such as an electric furnace, an RTA (a rapid thermal anneal) equipment, or the like in general.
As describing more specifically, at first an impurity, such as Si ion or the like, is implanted into a predetermined region regarding the semiconductor layer of the III group nitride compound, which is grown on a substrate, and then a film layer for coating such the semiconductor layer is formed by accumulating such as a dielectric film layer or the like over a whole surface for a device formation. Moreover, as a substance to be accumulated thereon in such the case thereof, it is able to make use of such as silicon oxide (SiO2), silicon nitride (SiN), aluminum nitride (AlN), or the like. Further, as a method for accumulating thereof, it is able to make use of such as a spattering method or the like. Next, the impurities becomes to be activated (the annealing process), which is implanted into the semiconductor layer of the III group nitride compound, which exists as an upper layer on the substrate, by performing a light irradiation process in a predetermined period of time for the substrate via such the film layer to be accumulated thereon. Furthermore, such the film layer to be accumulated thereby as mentioned above becomes to function as a prevention film layer for suppressing a number of N atoms to be come off from the semiconductor layer of the III group nitride compound in the period of such the annealing process.    [Patent Document 1] Japanese Patent Application Publication No. 2000-174034    [Nonpatent Document 1] Y. Irokawa et al., “Implantation temperature dependence of Si activation in AlGaN,” Appl. Phys. Lett. 88 (2006) 182106.    [Nonpatent Document 2] S. Matsunaga et al., “Silicon implantation in epitaxial GaN layers: Encapsulant annealing and electrical properties,” J. Appl. Phys. 95 (2004) 2461.    [Nonpatent Document 3] J. A. Fellows, “Electrical activation studies of GaN implanted with Si from low to high dose,” Appl. Phys. Lett. 80 (2002) 1930.
Here, a light to be made use regarding a general thermal treatment equipment is an infrared light, which has a wavelength as approximately between 0.6 μm and 1.0 μm. On the contrary, a band gap energy of the semiconductor layer to be formed with making use of the semiconductor of the III group nitride compound is larger than an energy of the above mentioned infrared light in general. Hence, according to an annealing step with making use of the infrared light, such the semiconductor layer to be formed with making use of the semiconductor of the III group nitride compound cannot help but function as a transparent film for the above mentioned infrared light. And then it becomes unable to perform a heat treatment directly for the impurity to be implanted into the semiconductor layer of the III group nitride compound.
For example, in a case where a GaN film layer is made use as the semiconductor layer of the III group nitride compound, a wavelength of a light, that the GaN layer adsorbs, is not longer than 365 nm approximately, due to the band gap energy of GaN as 3.4 eV. Hence, such the GaN film layer cannot help but function as a transparent film for the infrared light.
Thus, according to the above mentioned reasons, there is performed the heat treatment for the impurity to be implanted into the semiconductor layer as conventional, by heating up with making use of the light of such as the infrared light or the like for irradiating such as the substrate, a sample plate, or the like, via the semiconductor layer, that functions as the hyaline film layer, and then by raising temperature of such the semiconductor layer with making use of a conduction of heat therefrom.
However, according to such the method as described above to activate the impurity to be implanted into the semiconductor layer with making use of the conduction of heat from such as the substrate, the sample holder, or the like, it is required an excessively high temperature for the substrate. In particular for a configuration that the impurity is implanted into the layer to be spaced from such as the substrate, the sample holder, or the like, such as the MOSFET or the like, it becomes necessary to be the temperature for such the substrate as further higher for activating such the impurity.
And then in the case of setting the temperature for such the substrate in such the way, there are occurred problems, such as that atoms in a crystal thereof may become to be aggregated out on a surface of the semiconductor layer, that a crystalline defect may become to be formed on the surface of the semiconductor layer, which is called as a pit, or the like. Moreover, as the case may be, there are occurred further problems, such as that the semiconductor layer may become to be cracked, that a partial peeling off may become to be happened at between the semiconductor layer and the substrate, or the like.
Further, regarding the above mentioned problems, the aggregated atoms the atoms that constitute the semiconductor and the formation of the pit cannot help but occur even in a region where there is not any impurities to be implanted at all. Hence, in a case of fabricating the MOSFET by making use of the above mentioned conventional techniques for example, there are occurred problems, such as that a channel mobility would be decreased, that a withstand property thereof cannot help but become to be deteriorated thereby, or the like. Still further, in a case of fabricating the HEMTs (high electron mobility transistors), there becomes occurred another problem that a density of a two dimensional electron gas therein cannot help but become to be decreased thereby. Furthermore, in a case of producing a semiconductor laser, there becomes occurred another problem that an intermixing diffusion of the constitutive atoms or the impurities therein cannot help but become to be happened between a dielectric passivation layer and the semiconductor layer thereby.
Here, it is necessary to avoid such the above mentioned problems as much as possible, because of becoming a factor to decrease such as a performance, a reliability, or the like, regarding such a device. Moreover, it is not able to form a semiconductor device from the beginning thereof, in a case where any crack is generated therein, any partial peeling off is occurred therein, or the like.